Like so many famous songs of yore, "The Star-Spangled Banner" started as a poem, called “The Defence of Fort McHenry.” It was written by Francis Scott Key in 1814 during the War of 1812.

But his collection of fragments from the Star-Spangled Banner—one red swatch, one white—made him feel less like a have than a have-not. A friend possessed a blue scrap, and, without one for ...